Spinal Anchor Assemblies Having Extended Receivers

ABSTRACT

There are provided systems ( 40 ) and methods for positioning a connecting member ( 100 ) adjacent the spinal column that include one or more anchor assemblies ( 45 ) having an anchor ( 120 ) engageable to bony structure and an extended receiver ( 50 ) having a guide portion ( 54 ) and an implantation portion ( 52 ). A connecting member ( 100 ) is movable along the guide portion ( 54 ) from a location outside the patient to the implantation portion ( 52 ) in the patient, where the connecting member ( 100 ) is secured to the anchor assembly ( 45 ) with an engaging member ( 90 ). The guide portion ( 54 ) is formed as a single unit with but separable from the implantation portion ( 52 ) to provide a modified low-profile anchor assembly ( 45 ) after implantation of the connecting member ( 100 ).

BACKGROUND

Orthopedic devices such as spinal rods, plates, tethers, staples andother devices can be secured along the spinal column between one or morevertebral levels to stabilize the one or more vertebral levels. Whilesurgical procedures along the spinal column for placement of suchdevices are becoming less invasive, the decrease in space available inthe approach to the surgical site and at the surgical site for handlingand manipulating of the devices increases the difficulty in maneuvering,maintaining and finally positioning of the devices during the procedure.Furthermore, the small and intricate parts commonly associated with suchorthopedic devices can increase the difficulty of the installationprocedure. Accordingly, systems and devices which facilitate placementof orthopedic devices along the spinal column are desirable.

SUMMARY

There are provided systems and methods for positioning a connectingmember adjacent the spinal column that include at least two anchorassemblies having an anchor engageable to bony structure and an extendedreceiver having a guide portion and an implantation portion. Aconnecting member is movable along the guide portion from a locationoutside the patient to the implantation portion in the patient, wherethe connecting member is secured to the anchor assembly with an engagingmember. The guide portion is formed as a single unit with but separablefrom the implantation portion to provide a modified low-profile anchorassembly after implantation of the connecting member.

These and other aspects will be apparent from the following descriptionof the illustrated embodiments.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an elevation view a system for positioning a connecting memberalong the spinal column in a minimally invasive procedure.

FIG. 2 is a sectional view of an extended receiver comprising a portionof the system of FIG. 1.

FIG. 3 is a sectional view of a modified extended receiver and anchor ofan anchor assembly comprising a portion of the system of FIG. 1.

FIG. 4 is an elevation view of the system of FIG. 1 with a connectingmember positioned in the extended receivers of the anchor assemblies.

FIG. 5 is a plan view of the arrangement of FIG. 4.

FIG. 6 is an elevation view of the system of FIG. 1 with a connectingmember positioned in the implantation portions of the extended receiversof the anchor assemblies.

FIG. 7 is a perspective showing engaging members for positioning in theextended receivers to secure the connecting member in the implantationportions of the anchor assemblies.

FIG. 8 is a perspective of a portion of the system showing one of theengaging members positioned in one of the extended receivers to securethe connecting member in the implantation portions of the anchorassemblies.

FIG. 9 is the view of FIG. 8 showing the engaging member engaged to theimplantation portion of the extended receiver to secure the connectingmember therein.

FIG. 10 is the view of FIG. 9 showing a proximal break-off portion ofthe engaging member removed upon application of sufficient forcethereto.

FIG. 11 is the view of FIG. 10 with one of the arms of the extendedreceiver separated from the implantation portion at a break-off regiontherebetween.

FIG. 12 is the view of FIG. 11 with the other arm of the extendedreceiver separated from the implantation portion at a second break-offregion therebetween.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any such alterations and furthermodifications in the illustrated devices and described methods, and anysuch further applications of the principles of the invention asillustrated herein are contemplated as would normally occur to oneskilled in the art to which the invention relates.

Referring to FIG. 1 there is shown a system 40 for positioning aconnecting member 100 adjacent the spinal column in a minimally invasivesurgical procedure. Although system 40 is particularly suited forminimally invasive surgical procedures, it is not restricted to such.Furthermore, although its use and application is described with regardto spinal surgery, applications in surgeries other than spinal surgeryare also contemplated. In one form, system 40 provides at least a pairof anchors assemblies 45 including extended receivers 50 mounted toanchors 120 engaged to the spinal column. The extended receivers 50extend proximally from the anchors 120, and guide the placement of aconnecting member 100 from a position remote from the spinal column to aposition adjacent the spinal column. The extended receivers 50 areconfigured so that when the connecting member 100 is adjacent the spinalcolumn, connecting member 100 extends between the at least a pair ofanchors 120. The connecting member 100 can be secured to the anchorassemblies 45 and provide stabilization of the spinal column segment towhich the anchors 120 are attached. The extended receivers 50 can bemodified without invasively accessing the patient's body afterpositioning of connecting member 100 to provide the anchor assemblieswith a configuration suitable for post-operative implantation.

In one embodiment, each of the at least a pair of extended receivers 50includes a distal implantation portion 52 adjacent the respective anchor120 for receiving the connecting member 100 in an implantation positionto stabilize one or more vertebral levels. A proximal guide portion 54extends from opposite sides of the implantation portion 52 for guidingthe connecting member 100 from a location outside the patient to itsimplantation location in the implantation portion 52 adjacent theanchors 120. The guide portion 54 defines a channel therethrough thatopens along opposite sides of the extended receiver 50, and extends fromthe proximal end of the extended receiver 50 to the implantation portion52. In another embodiment, guide portion 54 is formed as a single unitwith implantation portion 52 portion at a break-off segmenttherebetween. The break-off segment provides a separation locationbetween the implantation portion 52 and the guide portion 54 so thatwhen sufficient force is applied to guide portion 54 it can be removedto modify the extended receiver 50 to an implantation configuration. Inanother embodiment, the at least a pair of anchor assemblies 45 includesthree anchor assemblies 45.

In one embodiment, the connecting member 100 is an elongated rod and theanchors 120 are bone screws. The bone screws can be a multi-axial typescrew positioned in the implantation portion 52 of extended receiver 50so that the receiver and bone screw are pivotal relative to one another.In another embodiment, the bone screws are non-pivotal or fixed relativeto the receiver. Connecting member 100 can be received in, on, or aboutthe implantation portion 52 of extended receiver 50 for engagementthereto. The connecting member 100 can be rigid, semi-rigid, flexible,elastic, non-compression load bearing, or of other suitable form forextending between and stabilizing adjacent portions of the spinal columnwhen secured thereto.

In FIG. 1, system 40 includes a first anchor assembly 45 a engaged tovertebra V1 and having a first extended receiver 50 a, a second anchorassembly 45 b engaged to vertebra V2 having a second extended receiver50 b, and a third anchor assembly 45 c engaged to vertebra V3 and havinga third extended receiver 50 c. Extended receivers 50 a, 50 b, and 50 care engaged to respective ones of a first anchor 120 a, a second anchor120 b and a third anchor 120 c, which are engageable to respective onesof three adjacent vertebrae V1, V2, V3, shown diagrammatically inFIG. 1. It should be understood, however, that the system and techniquesdiscussed herein may employ only two extended receivers and two anchors,or three or more extended receivers and anchors. Extended receivers 50a, 50 b, 50 c extend proximally from the respective anchors 120 a, 120b, 120 c through the tissue along the spinal column such that theirproximal ends project from or are adjacent the skin level S of thepatient for access by the surgeon. Extended receivers 50 a, 50 b, and 50c define a minimally invasive path for delivery of connecting member 100through the skin and tissue of the patient to the anchors engaged to thevertebrae. The minimally invasive path reduces and/or minimizes thetissue retraction and dissection required to accommodate delivery ofconnecting member 100 to the implantation location along the spinalcolumn where it provides the desired external stabilization of one ormore vertebral levels.

Referring now to FIG. 2, there is shown one embodiment of an extendedreceiver 50. Extended receiver 50 includes a lower or distalimplantation portion 52 and an upper or proximal guide portion 54extending along a central axis 51. Guide portion 54 includes a pair ofarms 55, 57 formed as a single unit with but removable from implantationportion 52 at break-off regions 56, 58, respectively. Receiver 50defines a general U-shape with a channel 62 extending therethroughtransversely to central axis 51. A lower through-hole 64 extends alongcentral axis 51 and opens at the bottom or distal end of implantationportion 52. In one embodiment, hole 64 is substantially perpendicular tochannel 62.

Implantation portion 52 forms a saddle that houses anchor 120 andreceives the connecting member 100 therethrough in an orthogonal ortransverse orientation to central axis 51 and in an orientationgenerally parallel with the spinal column. Implantation portion 52includes a pair of opposite side members 66, 68 sized and spaced toaccommodate elongate member 100 therein. Arms 55, 57 form an extensionof respective ones of the side members 66, 68, and are singularly formedtherewith at the respective break-off region 56, 58. Arms 55, 57 includea length extending proximally from side members 66, 68 so that theproximal ends of arms 55, 57 are located outside the patient when anchor120 is engaged to the spinal column. In one embodiment, this length isat least 30 millimeters. In another embodiment, the length of arms 55,57 is at least 50 millimeters.

As further shown in FIG. 3, side members 66, 68 each include an internalthread profile 67, 69 that threadingly engages an engaging member 90 (asdescribed below). Hole 64 is sized and shaped to receive and supportanchor 120 therethrough. Near the bottom of implantation portion 52,hole 64 is narrowed by a wall portion 70. Below wall portion 70, hole 64opens outwardly by virtue of a wall portion 72. Wall portion 72 allowsanchor 120 to be positioned in any of an infinite number of angularpositions relative to implantation portion 52 by reducing interferenceof the lower portion of implantation portion 52 with a shank portion 124of anchor 120, while a head portion 122 of anchor 120 is supported onwall portion 70. Other embodiments contemplate other engagementrelationships between the anchor 120 and receiver 50. In one embodiment,anchor 120 is formed as a single unit with receiver 50 and extends alongaxis 51 in a uni-axial arrangement. In another embodiment, anchor 120 iscaptured in receiver 50 with a split-ring washer, collar, or othersuitable retaining member. In still other embodiments, anchor 120 ispivotal in single plane, or in a predetermined number of planes,relative to receiver 50.

In the particular illustrated embodiment of implantation portion 52,implantation portion 52 includes an inner groove 74. As illustrated,groove 74 extends about side members 66, 68 and around hole 64. Groove74 is configured to accommodate snap ring 76 in a compressed condition.Groove 74 can have a height that is, in one form, greater than athickness of snap ring 76. Snap ring 76 can retain a crown 78 inimplantation portion 52 about the proximal side of head 122 of anchor120. Connecting member 100 is seated against crown 78 when secured inimplantation portion 52 with engaging member 90. In one embodiment,seating of crown 78 locks anchor 120 in position relative to extendedreceiver 50. In such an embodiment, crown 78 and/or head 122 can includeengagement structures that engage one another to provide the lockedarrangement. In a further embodiment, at least some motion between theconnecting member and anchor 120 is maintained by crown 78 whenconnecting member is secured in implantation portion 52. Still otherembodiments contemplate that crown 78 can be omitted and that theconnecting member 100 is seated directly against head 122 of anchor 120.

FIG. 3 further shows a modified anchor assembly 45′ where arms 55, 57have been severed at break-off regions 56, 58, forming modifiedbreak-off regions 56′, 58′. Arms 55, 57 are removed after placement ofconnecting member 100 into implantation portion 52 and securement ofengaging member 90 with internal threads 67, 69 of side members 66, 68.As shown in FIG. 2, arms 55, 57 can each include an internal threadprofile 80, 82, respectively, that is threadingly engageable by engagingmember 90 as it passes therethrough. The threaded engagement betweenarms 55, 57 and engaging member 90 provides a mechanical advantage inforcing connecting member 100 into implantation portion 52. Whenengaging member 90 is advanced distally into engagement with sidemembers 66, 68, the connecting member 100 is firmly seated against crown78, and engaging member 90 is secured to side members 66, 68

Referring now to FIGS. 4-12, various steps for implanting connectingmember 100 and securing it along the spinal column in a minimallyinvasive surgical procedure employing system 40 will be discussed. InFIG. 4, connecting member 100 is positioned through the aligned channels62 of extended receivers 50 a, 50 b, 50 c. As shown in FIG. 5,connecting member 100 fits within and maintains the channels 62 inalignment when it is positioned therebetween. For extenders havingmulti-axial capabilities, one or more of the extenders 50 a, 50 b, 50 ccan be pivoted toward and/or away from the others as may be desired tofacilitate placement of connecting member 100 therein. Connecting member100 is moved below the skin level S and toward the spinal column untilit is positioned in or adjacent implantation portions 52 of extendedreceivers 50, as shown in FIG. 6.

In FIG. 7 engaging members 90 a, 90 b, 90 c are provided for positioningthrough respective ones of the extended receivers 50 a, 50 b, 50 c.Engaging members 90 can be in the form of a set screw having a distalexternally threaded portion 92 and a proximal tool-engaging portion 94.Tool engaging portion 94 can be configured to break-off from distalportion 92 upon application of a sufficient force. Engaging members 90a, 90 b, 90 c can be secured to the respective implantation portions 52of extended receivers 50 to secure connecting element 100 to the anchorassemblies 45.

In FIG. 8, engaging member 90 a is shown in threaded engagement with theinternal threads along arms 55, 57 of guide portion 54 of extendedreceiver 50 a. In instances wherein connecting member 100 is not fullseated or positioned in implantation portion 52 of any one or more ofthe extended receivers, the respective engaging member 90 can act on theconnecting member and reduce or force it into position into theimplantation portion 52. The internal threads along arms 55, 57 providea mechanical advantage in advancing the connecting member into theimplanted position by bringing the vertebrae into alignment alongconnecting member 100. As shown in FIG. 9, engaging member 90 a contactsconnecting member 100 as engaging member 90 is threadingly advanced intoengagement with the internal threads along side members 66, 68 ofimplantation portion 52.

In FIG. 10 connecting element 100 is firmly seated in implantationportion 52 and sufficient torque applied to proximal portion 94 to severit from distal portion 92, providing a modified engaging member 90 a′.In this implanted position, engaging member 90 a′ can be recessed intoimplantation portion 52 so that it engages the threads along sidemembers 66, 68. In FIG. 11, arm 57 has been separated from implantationportion 52 by applying sufficient torque, twisting, bending or shearingforces to the proximal end of arm 57 to sever it at break-off region 58at side member 68. In FIG. 12, arm 55 has been separated fromimplantation portion 52 by applying sufficient removal force at theproximal end of arm 55 to sever it at break-off region 56 at side member66. Arms 55, 57 include sufficient rigidity along their length totransmit the removal force applied to the proximal end to the respectivebreak-off region with out twisting, deforming or severing at a locationproximal of the break-off region. This allows the minimally invasiveaccess to be maintained without tissue retraction to access arms 55, 57at locations within the patient to apply the removal force. Connectingmember 100 is thus secured for post-operative implantation to a modifiedanchor assembly 45 a′ having a suitably low profile for post-operativeimplantation. The other anchors assemblies 45 b, 45 c can be similarlymodified after securement of connecting member 100 therein to provide alow profile for system 40 extending from the spinal column.

Break-off regions 56, 58 provide an area of reduced wall thicknessadjacent the distal end of the respective arm 55, 57 that extendsbetween the arm 55, 57 and the respective side member 66, 68. Break-offregions 56, 58 can be located between the internal thread profilesdefined by side members 66, 68 and the adjacent arm 55, 57. In theillustrated embodiment, the outer surface of each of the break-offregions 56, 58 forms a concave depression or recess that extendscompletely about arm 55, 57 and the respective adjacent side member 66,68. Each of the arms 55, 57 is joined to the respective side member 66,68 with a break-off region having a wall thickness that is reducedcomparatively to an adjacent wall thickness of the respective arm andthe respective side member. Other embodiments contemplate othertechniques for reducing the wall thickness to provide a break-offregion, such as by providing perforations or undercuts between the arms55, 57 and the respective adjacent side member 66, 68. In any event, thebreak-off regions provide a separation location that is generallyuniform and substantially free of sharp of jagged edges after separationof the respective arms 55, 57. Other embodiments contemplate a break-offregion that is in a thread-free-zone.

It may also be desirable to provide a desired alignment betweenvertebrae by reducing the connecting member into the implantationportion of the extended receivers of the anchor assemblies. For example,the vertebrae may be misaligned as a result of spondylolisthesis,anatomical differences between the vertebrae, or some other condition.Also, there may be slight misalignments between the receiver membersthat make manually positioning the connecting member into each of thereceiver members difficult. In such situations, the engaging members 90can be employed to provide a mechanical advantage to seat the connectingmember in the implantation portions as the engaging members arethreadingly advanced along the arms 55, 57 and into the side members 66,68.

System 40 may employ various instruments to facilitate selection of theconnecting member, placement of the connecting member through theextenders and to the anchors, securement of the connecting member to theanchors, and manipulation of the vertebrae and/or anchors to a desiredposition or condition. For example, a driver can be provided that ispositionable through any one of the extended receivers to engage theanchor to the vertebra. A driver for positioning the engaging memberthrough the extended receiver and into engagement with the implantationportion can also be provided. A counter-torque device such as a wrenchor handle arm, can be secured to any one of the extended receivers tohold the extended receiver in position relative to the anchor attachedthereto as torque is applied to seat the engaging member into contactwith the connecting member in the implantation portion of the extenderreceiver. Compressors and distractors can also be provided to facilitateapplication of a compressive or distraction force between anchors beforefinal attachment of the connecting member to each anchor. Calipers canbe provided to measure a distance between the outermost extendedreceivers for sizing of the length of the connecting member to bepositioned between the anchors. A holding instrument can be providedthat is adapted to grasp and hold the connecting member placed betweenthe extenders, and can be employed to facilitate moving the connectingmember distally along the extenders toward and into the anchors. Areduction instrument can be provided that is positionable along or aboutthe extender receiver to provide a mechanical advantage for reduction ofthe connecting member into one or more of the implantation portions ofthe extended receivers.

Examples of suitable connecting members that extend between the anchorsinclude rods, wires, tethers, strands, cables, bands, plates, andstruts. The connecting member may include one component, or may includetwo or more components. One embodiment connecting member is shown inFIG. 1, and includes connecting member 100 having an elongatedrod-shaped body 102. Body 102 extends along a longitudinal axis 101between a first end 104 and an opposite second end 106. Body 102 iscurved about a radius formed by longitudinal axis 101. Ends 104, 106include generally the same size and shape, although such is notrequired. Other embodiments contemplate that body 102 is linear, acombination of linear and curved segments, a combination of linearsegments angled relative to one another, or a combination of segmentshaving differing curvatures. Body 102 has a uniform cross-section alongits length, which can be circular as shown. However, non-uniformcross-sections are also contemplated. In one embodiment, connectingmember is an elongated rod made from a metal alloy such as titanium.Other materials are also contemplated, including resorbable materials,non-resorbable material, polymers, elastomers, ceramics, other metalsand metal alloys, shape memory materials, bone and bone substitutematerial, composites, and combinations of materials.

Each of the anchor assemblies can be attached to the respective vertebrausing any one of a number of techniques. By way of example and notlimitation, one embodiment of a procedure contemplates an incision overthe target location of the spinal column, and that the skin and tissueare sequentially dilated to provide a minimally invasive pathway foranchor assembly insertion and engagement to each vertebra.

In another example procedure, a cannulated outer needle with an innerstylet can first be inserted to the targeted regions of the vertebrae,such as the pedicle in a posterior procedure, and aligned to provide thedesired trajectory into the pedicle. Alignment can be monitored andchecked with any viewing system, including radiographic, fluoroscopic,microscopic, endoscopic, loupes, naked eye, or any other suitableviewing system or instrument. After the cannulated needle and stylet areinserted into the vertebra, the inner stylet is withdrawn with thecannulated outer needle remaining engaged to the vertebra. A guidewireis positioned through the cannulated outer needle and engaged in thevertebra. The outer needle is then withdrawn so that the guidewireremains in place. The tissue around the guidewire is sequentiallydilated with a number of tubular dilators of increasing diameter. Whendesired opening size is obtained, the guidewire and inner dilators areremoved and the last inserted dilator provides a protected pathway tothe pedicle or other targeted portion of the vertebra. The anchorassembly can then be positioned through the dilated pathway and engagedto the vertebra. The procedure is then repeated to position the desirednumber of anchor assemblies, whether it be two, three or four or more.Incisions can be made between the adjacent anchor assemblies to providea pathway for insertion of the connecting member. Alternatively, theconnecting member can be inserted axially into one of the extendedreceivers and then manipulated below the skin and musculature byrotating it to extend between the anchor assemblies, avoiding incisionsthrough the skin and musculature between the anchor assemblies.

In another embodiment, the anchor assemblies are inserted percutaneouslywithout sequential dilation. The guidewire is positioned as discussedabove, and the anchor can be cannulated for positioning over theguidewire. The anchor and extended receivers are assembled and thenpositioned together over the guidewire, which guides the anchor assemblyto the pedicle or other targeted portion of the vertebra. A cannulateddriver tool is positioned over the guidewire and through the extendedreceiver to engage the head of the anchor and drive it into thevertebra.

In another embodiment, a pathway to the target location is prepared asdiscussed above. The guidewire and any dilators are removed. A cannulaor other suitable retractor may remain in the incision to provide aprotected pathway to the target location, although direct insertionthrough a micro-incision is also contemplated. An anchor driver isinserted through the extended receiver and engaged to the head of theanchor. The anchor driver can maintain the anchor in rigid alignmentwith the axis of the extended receiver if the anchor assembly ismulti-axial. The anchor and extended receiver are insertedpercutaneously to the target location of the vertebra, such as thepedicle. Insertion and alignment of the anchor assembly may be monitoredfluoroscopically or with any suitable surgical navigation system. Theanchor is then engaged to the vertebra at the target location with theextended receiver extending proximally therefrom through the skin levelof the patient. Anchor assembly insertion and engagement is repeated foreach vertebra along the instrumented levels.

In any embodiment, placement of the anchor assemblies can be conductedthrough a micro-incision, through a retracted opening formed in thetissue approaching the targeted location on the vertebra, or through atubular member providing a protected passageway to one or more of theadjacent vertebrae. It is also contemplated that nerve monitoring can beperformed through the extended receivers to guide placement of theanchors in the appropriate locations in the vertebrae. In oneembodiment, the anchor assemblies are engaged to pedicles of therespective vertebrae. Each pedicle can be drilled and, if necessary ordesired, tapped to receive a threaded screw portion of the anchorassembly. Formation and tapping of the holes in the pedicles can bemonitored with an electrical stimulus applied through a guidewire, tap,probe, or anchor driver prior to and during anchor assembly insertion.Response of the patient can be monitored to determine that anchorplacement does not impinge upon any nerves. The guidewire, tap, probe,driver or other instrument can be placed through a sleeve or dilatormade from plastic material to provide a non-conductive insulator. Instill a further form, an electrical signal is applied through the anchorassembly to guide placement of the anchor into the vertebrae withoutimpinging on neural structures. The extended receivers can be insulatedwith a protective, non-conductive coating, sleeve or other layer toprevent the current from straying.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, and that all changes andmodifications that come within the spirit of the invention are desiredto be protected.

1. A spinal surgical system, comprising: a connecting member includingan elongated body having a length sized to extend between at least twovertebrae; and an anchor assembly including a distal anchor engageableto bony structure and an extended receiver extending proximally from andpivotally coupled to said anchor, said extended receiver including adistal implantation portion adjacent said anchor sized and shaped toreceive said connecting member therein, said extended receiver furtherincluding a proximal guide portion including a pair of removable armsextending along a central axis, said arms extending proximally from andformed as a single unit with a respective one of a pair of opposite sidemembers of said implantation portion, said arms defining a channelextending therebetween from said implantation portion through proximalends of said pair of arms, said channel including a thread profile alongonly a distal portion of said arms, and said channel being sized andshaped to receive said connecting member through said proximal endopening thereof in a transverse orientation to said central axis.
 2. Thesystem of claim 1, wherein each of said arms is joined to saidrespective side member with a break-off region having a wall thicknessreduced comparatively to an adjacent wall thickness of said respectivearm and said respective side member.
 3. The system of claim 1, whereineach of said side members defines an internal thread profile along saidimplantation portion and each of said arms defines an internal threadprofile adjacent a distal end thereof that forms an extension of thethread profile of said side members.
 4. The system of claim 3, whereineach of said arms is joined to said respective side member at abreak-off region between said internal thread profile of said sidemembers and said internal thread profile of said arms.
 5. The system ofclaim 1, wherein said anchor includes a head pivotally captured in saidimplantation portion of said extended receiver, said anchor furtherincluding a shaft extending through a distal opening through saidimplantation portion for engaging the bony structure.
 6. The system ofclaim 5, further comprising a crown positioned about said head of saidanchor in said implantation portion.
 7. The system of claim 6, furthercomprising a second anchor assembly including a second distal anchorengageable to a second vertebra and a second extended receiver extendingproximally from and pivotal relative to said second anchor, said secondextended receiver including a distal implantation portion adjacent saidsecond anchor sized and shaped to receive said connecting membertherein, said second extended receiver further including a proximalguide portion including a pair of removable arms extending along acentral axis proximally from and formed as a single unit with arespective one of a pair of opposite side members of said implantationportion, said arms defining a channel extending therebetween from saidimplantation portion through proximal ends of said pair of arms, saidchannel being sized and shaped to receive said connecting member throughsaid proximal end opening thereof in a transverse orientation to saidcentral axis.
 8. The system of claim 7, wherein, for each of saidextended receivers, each of said side members defines an internal threadprofile along said implantation portion and each of said arms of saidrespective extended receiver defines an internal thread profile adjacenta distal end thereof that forms an extension of the thread profile ofsaid side members, and further comprising: first and second engagingmembers positionable in a respective one of said extended receivers tosecure said connecting member in said implantation portion thereof, eachof said engaging members including an externally threaded portionthreadingly engageable with said internal thread profiles along saidarms and said side members of said respective extended receiver.
 9. Thesystem of claim 7, wherein said connecting member includes a lengthsized to extend between at least three vertebrae and further comprisinga third anchor assembly including a third distal anchor engageable to athird vertebra and a third extended receiver extending proximally fromand pivotal relative to said third anchor, said third extended receiverincluding a distal implantation portion adjacent said third anchor sizedand shaped to receive said connecting member therein, said thirdextended receiver further including a proximal guide portion including apair of removable arms extending along a central axis proximally fromand formed as a single unit with a respective one of a pair of oppositeside members of said implantation portion, said arms defining a channelextending therebetween from said implantation portion through proximalends of said pair of arms, said channel being sized and shaped toreceive said connecting member through said proximal end opening thereofin a transverse orientation to said central axis.
 10. The system ofclaim 1, wherein each of said arms includes a length extending from saidrespective side member that is at least 30 millimeters. 11-22.(canceled)